The present invention relates to a method for performing electrospray mass spectrometric analysis and to an apparatus for performing the analysis.
Conventionally techniques related to such a technical field are described, for example, in the following literature:
(1) F. Bitsch, C. O. D. Buchecker, A. K. Khemiss, J. P. Sauvage, A. V. Dorsselaer, J. Am. Chem. Soc. 1991, 113, 4023-4025;
(2) D. C. Buchecker, E. Leize, J. F. Nierengarten, J. P. Sauvage, A. V. Dorsselaer, J. Chem. Soc., Chem. Commun. 1994, 2257-2258; and
(3) D. Whang, K. M. Park, J. Heo, P. Ashton, K. Kim, J. Am. Chem. Soc. 1998, 120, 4899-4900.
Liquid-introduction electrospray ionization (ESI) apparatuses have been developed so as to analyze molecular structures of biopolymers such as proteins; organometallic complexes; etc.
Organometallic compoundsxe2x80x94including highly-ordered supermolecules containing a transition metal that are formed through self-assemblyxe2x80x94have been of interest [See (1) F. Bitsch, C. O. D. Buchecker, A. K. Khemiss, J. P. Sauvage, A. V. Dorsselaer, J. Am. Chem. Soc. 1991, 113, 4023-4025; (2) D. C. Buchecker, E. Leize, J. F. Nierengarten, J. P. Sauvage, A. V. Dorsselaer, J. Chem. Soc., Chem. Commun. 1994, 2257-2258; (3) D. Whang, K. M. Park, J. Heo, P. Ashton, K. Kim, J. Am. Chem. Soc. 1998, 120, 4899-4900; and (4) M. Fujita, K. Ogura, Coord. Chem. Rev.; 1996, 148, 249-264.].
These compounds have been analyzed in terms of characteristics and detailed molecular structure, mainly through X-ray crystallography and nuclear magnetic resonance (NMR) spectroscopy.
However, single crystals having sufficient purity for allowing precise X-ray crystallographic structure analysis are generally difficult to obtain. For example, when molecules dissolved in the solution undergo rapid inter-transformation or contain metallic atoms exhibiting supermagnetism, NMR spectroscopy is not useful for characterizing molecules that are in a dissolved state. Mass spectrometry is another candidate method for effectively analyzing such metal complexes in the solution state. However, only a few cases of effective mass spectrometric analysis have been reported (see the aforementioned published literature (1) to (3)). Since these metal complexes are generally unstable against impact or heat for causing ionization, such poor stability of the complexes poses a problem, even when milder ionization through fast atom bombardment (FAB) or electrospray ionization (ESI) is employed.
In view of the foregoing, an object of the present invention is to provide a method for performing electrospray ionization mass spectrometric analysis, which method is capable of precisely analyzing the characteristics of unstable organometallic complexes. Another object of the invention is to provide an apparatus for performing the analysis.
To achieve the above objects, the present invention provides the following.
[1] a method for performing electrospray mass spectrometric analysis, characterized by comprising atomizing a sample solution to be analyzed which contains a solvent and is caused to flow out from a small-diameter tube for spraying while the sample solution is cooled by means of a gas for vaporization; and ionizing the atomized sample solution to be analyzed while a chamber for removing a solvent and an ion source shield are cooled, to thereby perform mass spectrometric analysis of the sample.
[2] a method for performing electrospray mass spectrometric analysis as described in [1], wherein the gas for vaporization and the ion source shield are maintained at low temperature within the range of liquid nitrogen temperature to room temperature.
[3] a method for performing electrospray mass spectrometric analysis as described in [1], wherein the sample to be analyzed is an organic compound.
[4] a method for performing electrospray mass spectrometric analysis as described in [1], wherein the gas for vaporization is a nebulizer gas.
[5] a method for performing electrospray mass spectrometric analysis as described in [1], wherein the gas for vaporization is an inert gas such as nitrogen gas.
[6] a method for performing electrospray ionization mass spectrometric analysis as described in [1], wherein water or a non-polar organic solvent (e.g., H2O, CH3CN, CHCl3) is used as the solvent, so as to perform molecular structure analysis.
[7] an apparatus for performing electrospray mass spectrometric analysis, characterized by comprising a small-diameter tube for spraying and for causing to flow out a sample solution to be analyzed containing a solvent; a sheath tube which is co-axially provided with the tube for spraying and allows passage of a gas for cooling; a chamber for removing a solvent and an ion source shield which are cooled; and a mass spectrometer for ionizing by use of the solvent and performing mass analysis of a sample to be analyzed; wherein an ion source formed through electrospraying is employed while the ion source is cooled by spraying liquid nitrogen directly to a chamber for removing a solvent and to an ion source shield.
[8] an apparatus for performing electrospray mass spectrometric analysis as described in [7], wherein the gas for cooling is introduced into the sheath tube after treatment in an apparatus for cooling an inert gas.